Field of the Disclosure
The disclosure relates generally solar-selective coatings. More specifically, the present disclosure relates to gradient SiNO anti-reflection layers in ceramic-metallic (cermet) solar selective coatings.
Background of the Technology
Generally, a solar selective coating is a kind of thermal collector configurable to harvest solar energy via a solar-thermal conversion route. Conventionally, it is understood that a selective absorber with a high solar absorptance (α) in the wavelength range of about 0.3 μm to about 2.5 μm of the solar spectrum and a low thermal emittance (ε) at the operational temperature in the wavelength range beyond 2.5 μm in the thermal region may cater to the requirements of enhanced photo-thermal conversion efficiency. Theoretically, an ideal solar absorber should have zero reflectance over solar spectrum region and zero thermal emittance.
Commercial investigation into solar absorber/spectrally selective coatings and various applications therefore has been conducted over the last 55 years. The investigations have identified and commercialized black chrome coatings for solar hot water applications. Black chrome may be considered as a successful commercial selective coating material and it has an absorptance (α) of about 0.90 μm to about 0.95 μm and an emittance (ε) of about 0.1 μm to about 0.2 μm. In most applications, the black chrome is electroplated onto an application.
However, the poor or high thermal emittance properties have restrained the widespread incorporation of black chrome into commercial products. Additionally, the environmental concerns and regulations associated with electroplating have provided a disincentive for further development of the black chrome coatings. Thus, solar selective coatings with high solar absorptance, low thermal emittance, and low reflectance are sought for commercial applications.